He proposed a universal toise (French: Toise universelle) which was twice the length of the seconds pendulum. He found the value of 440.5 lines of the Toise of Châtelet which had been recently renewed. In 1671 Jean Picard measured the length of a "seconds pendulum" at the Paris Observatory. In 1645 Giovanni Battista Riccioli had been the first to determine the length of a " seconds pendulum" (a pendulum with a half-period of one second). Nevertheless, with the increasing scientific activity of the 17th century came calls for the institution of a standard measure or " metro cattolico" (as Italian Tito Livio Burattini said ), which would be based on natural phenomena rather than royal decree, and would also be decimal rather than using the various systems of subdivision, often duodecimal, which coexisted at the time. Indeed, as the measures were often used as the basis for taxation (of cloth, for example), the use of a particular measure was associated with the sovereignty of a given ruler and often dictated by law. The standard measures of length in Europe diverged from one another after the fall of the Carolingian Empire (around 888): while measures could be standardised within a given jurisdiction (which was often little more than a single market town), there were numerous variations of measure between regions. Giovanni Domenico Cassini, with the Paris Observatory in the background Where older traditional length measures are still used, they are now defined in terms of the metre – for example the yard has since 1959 officially been defined as exactly 0.9144 metre. It is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299 792 458 when expressed in the unit m⋅s −1, where the second is defined in terms of the caesium frequency Δ ν Cs.ĭuring the mid nineteenth century the metre gained adoption worldwide, particularly in scientific usage, and it was officially established as an international measurement unit by the Metre Convention of 1875. In 1983 this was updated to a length defined in terms of the speed of light this definition was reworded in 2019: The metre, symbol m, is the SI unit of length. Progress in science finally allowed the definition of the metre to be dematerialized thus in 1960 a new definition based on a specific number of wavelengths of light from a specific transition in krypton-86 allowed the standard to be universally available by measurement. The comparison of the new prototypes of the metre with each other and with the Committee metre (French: Mètre des Archives) involved the development of a special measuring equipment and the definition of a reproducible temperature scale. This in turn was replaced in 1889 at the initiative of the International Geodetic Association by thirty platinum-iridium bars kept across the globe.
A new unit of length, the metre was introduced – defined as one ten-millionth of the shortest distance from the North Pole to the equator passing through Paris, assuming an Earth's flattening of 1/334.įor practical purposes however, the standard metre was made available in the form of a platinum bar held in Paris. As a base unit of length, many scientists had favoured the seconds pendulum (a pendulum with a half-period of one second) one century earlier, but this was rejected as it had been discovered that this length varied from place to place with local gravity, and that it could complement meridian arc measurements in determining the figure of the Earth. With the French Revolution (1789) came a desire to replace many features of the Ancien Régime, including the traditional units of measure. Rather than the various complex systems of subdivision then in use, they also preferred a decimal system to ease their calculations. Increasingly accurate measurements were required, and scientists looked for measures that were universal and could be based on natural phenomena rather than royal decree or physical prototypes.
The history of the metre starts with the Scientific Revolution that is considered to have begun with Nicolaus Copernicus's publication of De revolutionibus orbium coelestium in 1543. An early definition of the metre was one ten-millionth of the Earth quadrant, the distance from the North Pole to the Equator, measured along a meridian through Paris.
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